In a switching power-supply device configured to perform an output voltage control by a switching operation of a switching element connected to an inductor, a discontinuous mode, where the switching element is turned off and is then turned on after the current flowing through the inductor becomes zero, and a continuous mode, where the switching element is turned off and is then turned on before discharging of the accumulated energy of the inductor is completed and thus the current is enabled to continuously flow through the inductor are switched, depending on an input voltage and a state of load.